Elemental bromine is used in the manufacture of a variety of bromine compounds of commercial interest. It is also used, either directly or indirectly, in the desizing of cotton, for bleaching pulp and paper, in hair waving compositions, as a biocide (e.g. water disinfection) in air conditioning absorption fluids and as an etchant. A number of these applications require the use of aqueous solutions containing bromine. However, such use is limited due to the relatively low solubility of bromine in water, which is not influenced significantly by temperature (Kirk-Othmer, Encyclopedia of Chemical Technology, Vol 4, p. 229):
TABLE 1 ______________________________________ TEMP. .degree.C. SOLUBILITY, g/100 g SOLN ______________________________________ 5 3.54 10 3.60 20 3.41 25 3.35 40 3.33 53.6 (bp) 3.50 ______________________________________
It is unwieldy to transport such dilute solutions and the formation of bromine solutions in water on site presents a variety of technological problems. Thus for example, not only is the solubility of bromine in water low, its rate of dissolution is also low. Bromine is also both volatile and corrosive. Furthermore, at low temperatures, metastable aqueous solutions of bromine in water may be formed. It is therefore of interest to provide a means by which bromine itself or a bromine concentrate can be made available and transported in a readily diluted form for use in these various applications.
To overcome the aforesaid difficulties, it has been suggested to increase the solubility in water by the addition of salts or mineral acids. The following are some examples, at 25.degree. C. (Kirk-Othmer, Vol 4, p. 229):
TABLE 2 ______________________________________ SOLUTE SOLUTE, g/l SOLN BROMINE, g/l SOLN ______________________________________ none 34.0 KBr 119.0 216.0 NaBr 320.0 546.0 NaCl 58.5 55.9 Na2SO4 63.6 23.9 HBr (20.8.degree. C.) 33.7 108.8 HCl (20.8.degree. C.) 39.0 79.2 ______________________________________
The bromides are seen to be particularly effective due to the formation of complexes in these systems.
However, increasing the solubility of bromine in water in this manner suffers from the nature of the solubilizers themselves. Thus, for example, high salt or acid concentrations cannot be tolerated by many systems. In addition, an ecological waste problem is presented by the need to dispose of the brine or acid solutions which remain after the bromine, originally contained therein, has been used. In some applications involving emulsified systems, such as paint latexes, high salt concentrations can break the emulsions.
Because of these problems, the use of bromine dissolved in other solvents is common, though these are more costly per se, introduce additional costs in solvent recovery, purification and recycling operations, and may even be dangerous. Thus for
example, solutions of bromine in methanol are widely used in the etching of semi-conductor materials, in spite of the fact that there is a potential hazard in preparing such solutions [P.T. Bowman, et al, J. Electrochem. Soc. 137 (4), 1309 (1990)].
It is a purpose of this invention to provide aqueous solutions of bromine that are free from objectionable salt or acid components.
It is another purpose of the invention to achieve rapid dissolution of bromine in water.
It is a further purpose to achieve the aforesaid purposes by means which are inexpensive, compatible with a wide variety of applications, safe and ecologically friendly.
It is a further purpose to provide means for the safe and economical transportation of elemental bromine, which means further permit easy recovery and use of the bromine in situ.
It is a still further purpose to provide a convenient and inexpensive solution that is adapted for use as bromination means.
It is a still further purpose to provide a convenient and inexpensive solution that is adapted for use as bleaching, disinfection and etching means and the like.
Other purposes and advantages of the invention will appear as the description proceeds.